1. Field of the Invention
The present invention relates to communication method and system and a control device for controlling communications when a radio terminal moves between areas in the radio communication such as that of the CDMA scheme that is carried out between a mobile radio terminal and a radio base station
2. Description of the Related Art
In the radio communications using the CDMA scheme, the radio terminal measures a receiving quality of control signals transmitted by the other radio base stations with which it is currently not in communication, according to a command of a control device or a judgement of the radio terminal. This receiving quality may include a receiving power and a signal to noise ratio.
Also, in the conventional radio communication such as that of the CDMA scheme, the radio base station transmits the identical control signals to the radio terminals located inside its controlling area, while also transmitting communication signals as signals for speech communication (data communication), and the control device adopts a scheme for code division multiplexing the communication signals with the control signals according to the need.
However, at a time of the handover in which the radio terminal moves to another neighboring area, the radio terminal is going to receive the control signals transmitted by the radio base station which controls a moving target area, and at that point, if the other communication signals are code division multiplexed in the same time-slots as the received control signals at the moving target area, there has been a problem that the receiving quality of the control signals transmitted from the radio base station at the moving target area will be degraded.
Here, in order to prevent the degradation of the receiving quality at a time of the handover, it is also possible to use a scheme for not code division multiplexing any other signals with the control signals, but this scheme has a problem that the number of available time-slots is reduced so that the communication capacity of the entire communication system becomes small.